1. Field of the Invention
The present invention relates to an electronic multilayer ceramic component such as a multilayer capacitor, and more particularly to an electronic multilayer ceramic component in which the relationship between the size of a region in which inner electrodes are disposed in a multilayer fashion and the size of a part located outside that region is optimized.
2. Description of the Related Art
Electronic multilayer ceramic components, such as a multilayer capacitors are becoming increasingly smaller. Electronic multilayer ceramic components are constructed such that a plurality of inner electrodes are embedded in a sintered ceramic block, and outer electrodes are formed on outer side faces of the sintered ceramic block. With the reduction in size of electronic multilayer ceramic components, the size of the sintered ceramic block has become very small. For example, various types of sintered ceramic blocks with sizes smaller than 1.6 mmxc3x97 0.8 mmxc3x970.8 mm are commercially available.
In the case of multilayer ceramic capacitors, in order to reduce the size while maintaining the capacitance at a large value, the thickness of ceramic layers between adjacent inner electrodes is selected to be as small as 5 xcexcm or 3 xcexcm or still smaller, and as many as several hundred inner electrode layers are used.
FIG. 2 is a cross-sectional view of a conventional multilayer capacitor of the above-described type. As shown in FIG. 2, the multilayer capacitor 51 includes a plurality of inner electrodes 53 disposed in a sintered ceramic block 52 such that the plurality of inner electrodes 53 overlap with one another via ceramic layers. In order to achieve a greater capacitance with a smaller size, various attempts have been made to dispose a greater number of inner electrode layers within a sintered ceramic block with a smaller size.
To this end, the thickness G of outermost ceramic layers 52a and 52b parallel to the inner electrodes and located outside a region in which the plurality of inner electrodes 53 are laminated, is set to be as small as possible. However, if the thickness G of the outermost ceramic layers 52a and 52b is less than 100 xcexcm, there is a possibility that the outermost ceramic layers 52a and 52b delaminate at an interface with an inner electrode 53 during a sintering process in which ceramic layers are sintered into a single block 52. For the above reason, the lower limit of the thickness of the outermost ceramic layers 52a and 52b is about 100 xcexcm.
It is also required to minimize the width WG of a side gap region between side ends 53c of the inner electrodes 53 and an end face 52c of the sintered ceramic block 52. To this end, the ratio WG/EW is generally set to a value smaller than 0.3 where EW is the width of each inner electrode 53.
In the conventional multilayer capacitor 51, as described above, in order to obtain a greater capacitance with a smaller size, it has been attempted to minimize the thickness G of the outermost ceramic layers 52a and 52b and also minimize the ratio WG/EW.
However, when the size of the sintered ceramic block 52 is further reduced, if the ratio WG/EW is smaller than 0.3 and if G is set to be about 100xcexcm, various problems occur as described below. That is, during the sintering process for obtaining the sintered ceramic block 52, a density difference occurs between a ceramic region in which a plurality of inner electrodes 53 are laminated via ceramic layers and outer ceramic regions, that is, the outermost ceramic layers 52a and 52b. The density difference results in a stress which can produce cracks or delamination in the sintered ceramic block 52.
In a thermal shock test in which multilayer ceramic capacitors are subjected to abrupt temperature changes or in other reliability tests, a crack or delamination occurs in some samples due to the stress caused by the difference in thermal expansion coefficient between the inner electrodes and the ceramic.
Thus, in view of the above problems in the conventional technique, it is an object of the present invention to provide an electronic multilayer ceramic component which is less susceptible to having a crack or delamination and thus has high reliability and high resistance to thermal shock.
According to an aspect of the present invention, there is provided an electronic multilayer ceramic component comprising: a sintered ceramic block having a first end face, a second end face, upper and lower surfaces connecting said first and second end faces to each other, and a pair of side faces; a plurality of inner electrodes disposed in the sintered ceramic block such that the plurality of inner electrodes overlap in a thickness direction with one another via ceramic layers and such that each inner electrode extends from the first end face toward the second end face but not reaching the second end face or from the second end face toward the first end face but not reaching the first end face; and a first outer electrode and a second outer electrode formed such that the first and second end faces are covered with the first and second outer electrodes, respectively; wherein, when the width of the region in which the plurality of inner electrodes are disposed such that the inner electrodes overlap in the thickness direction with one another via ceramic layers is denoted by EW, the width of a side gap region between ends of the inner electrodes and one of side faces of the sintered ceramic block is denoted by WG, the thickness of a region in which the plurality of inner electrodes are disposed such that the inner electrodes overlap in the thickness direction with one another via ceramic layers is denoted by T, and the thickness of one of the outermost ceramic layers parallel to the plurality of inner electrodes and located outside the region in which the plurality of inner electrodes are disposed such that the inner electrodes overlap in the thickness direction with one another via ceramic layers is denoted by G, the following conditions are satisfied:
WG/EWxe2x89xa70.3,
and
T/Gxe2x89xa67.0.
In the electronic multilayer ceramic component according to the present invention, the sintered ceramic block preferably has a size equal to or less than 1.6 mm in length, 0.8 mm in width, and 0.8 mm in thickness.
Furthermore, in the electronic multilayer ceramic component according to the present invention, the sintered ceramic block may be made of a dielectric ceramic material so that a multilayer capacitor is formed.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.